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DIY HPF Stompbox?

Discussion in 'Effects [BG]' started by leonard, Jan 14, 2017.

  1. leonard


    Jul 31, 2001
    In this world full of breadboard stompbox designs there is no hi-pass filter design for us bassists. I could build one but I can't design it. I know there are people here who could design one with ease.

    How to build one?

    The Fdeck units might be nice and affordable, I know, but they are out of my reach because I live in another continent.

    My Weller is on.
    gregmon79 likes this.
  2. leonard


    Jul 31, 2001
    Last edited: Jan 14, 2017
    Duder likes this.
  3. Dominic DeCosa and leonard like this.
  4. leonard


    Jul 31, 2001
    gregmon79 and Bugeyed Earl like this.
  5. leonard


    Jul 31, 2001
    What is the input impedance of this? 10 megaohms? It can be thought of as a buffer, phase switch and hi-pass filter at the same time?
  6. Yes
    leonard likes this.

  7. Here you go, tagboardeffects has the layout below and a whole lot more-roar:


    I believe @johnk_10 has a verofied layout for this as well.

    PS: WHOOPS — Bugeyed Earl beat me to the punch and I missed it!
    leonard likes this.
  8. suscribed
  9. BadExample


    Jan 21, 2016
    Stop the press! I hate to be that guy, but I might be about to drop a deuce on this fine parade :( I always feel for people who have to buy something from across the pond and have the snot taxed out of it after the snot has been taxed out of it here, plus shipping.

    Also, I want to be clear, I am not disrespectful of anyone's technical skills. I'm sure OP and those who have responded are above average with tech stuff, and may or may not have developed that talent into schematic/component level troubleshooting.

    As much as @fdeck has not only graciously offered up his design work for free, and even gone as far as testing alternate parts and shows how to solder SMT FETs by hand, I would advise to make sure you can get the FETs shown in that layout before spending any money on other parts. If you cannot get the correct FETs, it would be advisable to read all three documents on his updated google site located under Technical & DIY Stuff - hpftechllc ! It's been 5 careers and up to a zillion years ago since I've done any design or repair work with FETs, and even then it was using them as switches for DC motor control. So, I don't know if you need to fiddle with component values to get the alternate parts to work. This could be a show stopper if the builder can not troubleshoot by schematic. I fear building by layout may not be an option if the FETs are not available and in the same package type. SMT can probably be done by study of Fdeck's process and making an adapter board or extending the current board to accept the FETs. Of course a friend lending a hand at some of the details could work as well.

    No friends? (OK that was a jab/insult :laugh: ) I've taken a few brush up classes at the local 2 year tech school, and they always love having something that ties into the real world to work on in labs, including the instructors, of of which were engineering staff or instructors at the local engineering university during the day. I've also found university staff to be helpful. Beer bribes work :D

    If the FET's are still available in the US, perhaps ordering and asking the seller to ship as a gift under $5 value or something. Or ship to one of us to reship if they won't do that. At least you can hide from the VAT man. If I am called upon to reship and it's under maybe $20 (depending on my girly mood swing at the time :D ), I would probably just ask you do a similar favor for someone else. Maybe give a wino a cheap bottle and a pack of smokes or something.

    For SMT, I think this:


    plus this:


    Then jump G, D, S to the corresponding locations on the perf board layout. See Quick and Dirty JFET Buffer, Rev. 2 - hpftechllc for instructions and details.

    Finally, beware of static electricity (ESD). I mention this as an awareness and not full go paranoia. FETs are generally very sensitive to ESD, some more than others. Presumably these are not super-sensitive since Fdeck does not mention it, but with obsoleted components, they can become pre-damaged, or one can damage the parts handling them without ESD protection. Unfortunately, the result is not always a dead part on the spot. Typically I saw noisy FET input op-amps, or the walking wounded/walking dead that come back to haunt you with noise of failure. If that does not apply to JFETs, that would be good to know, but as a general minimal precaution, it's a good idea to discharge static from yourself and work on a sheet of foil placed on the bench. If you choose to ground yourself or the foil, be sure to use a 1 to 10M OHM resistor in the path to ground for safety. Even then, the foil is only safe to use for soldering unpowered circuts. You only get to die once, so don't make it be from any of my BadExample advice! Most components are pretty safe from ESD once in circuit. GFCI.

    I am sorry if any of this puts an end to this plan.
    joe vegas likes this.
  10. leonard


    Jul 31, 2001
    Ok, so some of the parts might be obsolete? I'm definitely not going to make anything with SMT FETs. Modifying the circuit to take a different FET is out of my skill level too.

    I have a friend but he's a guitarist. He can't help me with anything.

    The local store carries these transistors:

    FET RF 2N4416 - PARTCO verkkokauppa

    TRANSISTOR 2N4403 - PARTCO verkkokauppa

    Maybe there's still a chance of building this?
    Last edited: Jan 14, 2017
    Microbass and Stumbo like this.
  11. BadExample


    Jan 21, 2016

    Those look fine to me. On the FET, not sure what the RF is, but Radio Frequency is a good guess. That might explain the metal can. I can't get the data sheet to open, probably due to my security settings. Can you see it? Metal can is good. RF is not necessarily bad, unless there are internal changes that would effect audio.

    I'll try to get the datasheet to open on a less secure computer, assuming no one beats me to it and offers advice.


    Until I opened the big image, I thought the wire coming off was a ground ring. It looks to me like it might be for ESD. If it touches all the pins as it appears to in the larger pic, it probably is for ESD and can be pulled off after soldering in place. You will need the datasheet, but the op amps and other metal canned parts I've worked with marks the highest numbered pin, rather than the lowest (pin 1) as is common on plastic DIP packages. You can easily get the pins lined up to match the layout. Just slip on some insulation (tiny heatshrink if you have it or just some insulation stripped from slightly larger size wire), then form to shape with two pairs of needle nose pliers, trim to equal length if needed. You just need to look up what pin is what and bend them to be D, S, G in a fairly straight line. Does not need to be perfect, because you can just flex during insertion. Hmmm, sounds dirty. 4th pin is probably ground for the can. I think if ground is earthed, it's good to ground it, but most likely ground will float and then it should just be snipped off. Take others advice on this if offered. That goes for grounding as well as use of the "RF" part.

    On the standard transistor in the plastic case, it doesn't hurt to look at the datasheet and verify the pin order.

    It might not be a bad idea to socket these. If you wish to do so, let me know and I'll explain how to do this for less than the price of the JFET you found. I think you have a good chance of success here, and a spare or two of the FETs, plus socketing with good machined type sockets will ensure you can replace those easily years down the road if they fail.

    If you can't see the datasheets, you might ask the seller for copies or a link. IDK how to determine the pinout of the FET without a datasheet. The transistor can be verified by a DVM with a diode checker, commonly known as "That beepy wire checker thing."
    leonard likes this.
  12. No, the parts are not obsolete. If you can get those parts locally, you'll be fine.

    The fDeck was specifically designed as a buffer/HPF for upright bass. It's fine to use on a pedal board, but it's quite a bit overkill for that purpose. If you're putting it after anything else on the board, for example, you probably want to drop that 10Meg down quite a bit. Maybe 220k (low-Z into 10Meg could contribute to noise down the line when you add gain after the HPF). Probably don't need the phase switch, either, unless you have pedals that reverse the phase that you'd like to correct. The volume control might be useful, or it could just be another knob to get tweaked when you least expect it.

    Otherwise, have fun!
    leonard likes this.
  13. BadExample


    Jan 21, 2016
    By obsolete, we don't mean not useful, just means out of production, which may or may not mean hard to find. I have made no investigation on my own to determine if the parts in the layout are out of production, and I apologize if these are not in that status and I have caused any concern.

    Speed in reply is over rated. In fact I hear it can lead to bug eye syndrome!
  14. BadExample


    Jan 21, 2016
    Good tips. Asking due to my ignorance of discrete FET based filtering, does changing the 10M require any adjustment to the other input components (R1, C1, C2)? I need to re-read Fdeck's information :D
  15. leonard


    Jul 31, 2001
    I can't find no datasheet. Only this:

    Applications include: VHF High-Frequency Amplifier/Mixer, Oscillator, Sample-and-Hold, Very Low Capacitance, Switches."

    I might ask for one from them. The component is quite useless without it.

    I play some upright too. And I'd like to use my pedalboard with both the electric and upright. It would be the first thing on my board. 10Meg is pretty much compared to 500k on my Markbass or 1Meg on my TU-2. The phase switch is gonna be handy. Actually a very useful pedal if I ever can make it.
  16. johnk_10

    johnk_10 vintage bass nut Supporting Member Commercial User

    Feb 16, 2008
    Thousand Oaks, CA
    John K Custom Basses
    i drew up a veroboard layout and built one and it works perfect:

    Stumbo and leonard like this.
  17. boomertech

    boomertech Frank Appleton Supporting Member Commercial User

    Apr 8, 2009
    Syracuse, NY
    Designer/Owner of FEA Labs
    The 10Meg resistor noise will be swamped out by the low-Z of anything plugged into the input. So, it shouldn't be an issue. If you really wanted a lower-Z for everything but piezo pickups, you could put a toggle switch in there for switching in different values of R2 and size C1 for the lowest value of R2 for your low end roll-off.

    leonard and lowfreqgeek like this.
  18. leonard


    Jul 31, 2001
  19. 9Thumbs


    Jul 3, 2013
    Near Boston
    Since the electronics wizards seem to be here, I have an FDeck series 2. It is wonderful as a High Pass Filter. I also use the phase switch which definitely helps with my upright. What I just don't understand is the impedence deal. The HPF, when both knobs are turned up all the way(full volume, minimum HPF) the tone and volume seem to stay the same, with or without the FDeck. What does the difference of impedence between the piezo and my amp do?

    Thanks for any thing you can tell me

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